The present invention relates to a current detection device and a method for sensing an electric current. The present invention particularly relates to a current detection device and a method for sensing an electric current in a measuring path, which conducts a current that corresponds to an electric current in a power path.
Although the present invention is described in connection with IGBTs, which have a sense connection, said present invention can furthermore be used for any other applications in which a current is to be evaluated in another current path which corresponds to the current in a power path.
The American patent publication U.S. Pat. No. 5,877,617 A discloses a circuit arrangement in which a load is supplied with current in a current path. The circuit arrangement furthermore comprises an additional transistor which provides a current that corresponds to this current for the load. The current that is provided via the additional transistor is used to monitor and evaluate the current flow for the load.
Bipolar transistors with an insulated gate (IGBT) are furthermore known, for example, for measuring and evaluating a current through a semiconductor switch. In the case of such bipolar transistors, a current is provided at an additional sense connection which is proportional to the main current through the semiconductor switch. The current from the sense connection is less than the main current in the emitter path of the IGBT by an approximately constant factor.
The circuit arrangement for evaluating the current in the sense path of such an IGBT has to be dimensioned for the maximum duty cycle of the IGBT and also for the maximally occurring currents. In this case, relatively large currents can even occur in the sense path, in particular in the event of a fault.
There is therefore the need for an improved evaluation circuit for a circuit arrangement in which a current evaluation takes place via a separate measuring path. There is particularly a need for a current evaluation circuit which is also not overloaded when larger currents occur in the measuring path.